Field
The present disclosure relates to a tread for a tire of the snow tire type. More particularly, the disclosure relates to a snow tire having improved end-of-life grip performance.
Description of Related Art
A tire for winter driving, referred to as a snow tire, comprises in the way known per se a tread that is provided with a plurality of sipe incisions. This addition of sipes to the tread of a tire has notably been disclosed in document FR759592 and its addition FR43383.
The sipes delimit on the tread blades of rubber which have edge corners capable of biting into the snow when driving on snowy surfaces, thus improving grip on this road surface. The action of the edge corners on the road surface is all the greater when the tread is new. This is because in that condition, the blades of rubber have a high slenderness ratio, that is to say a great height for a small width relative to this height. Thus, as the blades enter the contact patch in which the tire is in contact with the road surface these blades tilt. The pressures that the edge corners of the blades apply to the road surface are therefore increased. Such a phenomenon is notably illustrated in FIG. 3 of document FR2418719.
With tread wear, the height of the blades decreases and the deformation of these blades, as they enter the contact patch, likewise decreases. As a result, the biting effect of the edge corners decreases with tread wear.
In order to maintain good grip of a snow tire, even at an advanced level of wear, document EP0378090 has proposed providing the tread of this tire with complex sipes which duplicate from a certain depth onwards. Viewed in cross section, each of these sipes has a rectilinear first part extending radially into the tread and a second part extending the first part and comprising two branches. With such a configuration, the density of the sipes on the tread at the end of its life is greater than the density of the sipes of this tread at the beginning of its life, making it possible to increase accordingly the number of edge corners and therefore the grip of this tire when its wear reaches a certain level.
In order to improve the end-of-life grip of this tire still further it is possible to insert, between the complex sipes, simple sipes which extend in a rectilinear manner into the depth of the tread, as illustrated in FIG. 4 of document EP0378090. However, by increasing the number of sipes in the tread, the space occupied by the blades of rubber between these sipes is correspondingly reduced. The mechanical integrity of these blades is therefore reduced and the risk of chunking of all or part of these blades during operation of the tire is increased.
There is therefore a need to improve the grip of snow tires, notably at the end of life, while at the same time maintaining or even improving the overall mechanical strength thereof.